Method of coating a substrate with a plastic material



Mardh 31, 1910 3,503,778

METHOTYOFCOATING A SUBSTRATE WITH A PLASTIC MATERIAL H. o. CORBETT ET A2 Sheets-Sheet 1 Filed Oct. 30, 1967 INVENTORS HERBERT O. CORBETT JOHNJ. QUACKENBUSH v ATTORNEY March 31, 1970 o, co -r ET AL 3,503,778

METHOD OF COATING A SUBSTRATE WITH A PLASTIC MATERIAL 2 Sheets-Sheet 2Filed Oct. 30, 1967 FIG. 2

JOHN J QUACKENBUSH United States Patent US. Cl. 117--21 4 ClaimsABSTRACT OF THE DISCLOSURE A'substrate is coated by a process comprisinggenerating a dust cloud of very finely divided plastic powder,preheating the substrate, causing the dust cloud to settle underquasi-equilibrium conditions onto the substrate and further heating thecoated substrate to effect fusion of the plastic powder.

This application is a continuation-in-part application of US.application Ser. No. 542,040 (now US. Patent 3,354,865) filed Apr. 12,1966, entitled Cloud Dispersion of Fine Plastic Powders in the names ofQuackenbush and Corbett, and is a division of application Ser. No.555,543 (now US. Patent 3,359,944) filed June 6, 1966, by these sameinventors, both of these applications being assigned to the presentassignee.

The powder coating of webs of plastic material or paper, or the like, iswell known to the art. In such arrangements, a stationary or moving baseweb is to have deposited or dusted thereon a suitable powder with theweb and powder later being operated upon to cause the thermoplasticparticles to melt and fuse to the web. Thus, the coated web can bepassed through an oven and sub jected to temperatures which will causethe thermoplastic particles to melt and fuse to form an intimate bondand a continuous or non-continuous type coated surface, as desired.

The materials can be further press-nipped under pressure as by heatedrolls to force the particles down into the web and provide high glosssurfaces or intimate bonding of fibers or fiber-like materials.

Considerable difficulty has been experienced in the past to properlysuspend and evenly deposit very finely ground thermoplastic powders ofvarying densities (in the range of .910 to .965) and varying particlesizes (from 2 to 100 microns).

The present invention provides a novel apparatus for providing a dustcloud of diverse particle sizes and densities in the dry form. Thiscloud of material is then deposited on a suitable movable or stationaryweb in an even manner with controlled feed and dispersion levels andgood control over the complete deposition process. The dry coating lineconstructed in accordance with the invention will consist of four majorcomponents: a preheat oven, a settling chamber, a fusing oven, and adust cloud generating device.

The preheat oven will contain a suitable heating structure such as a2160 watt fused quartz edge compensated heater in an insulated chamber.The web upon which dust is to be deposited is then moved through thischamber so that its surface will be heated to some predetermined levelwhich is somewhat below the minimum temperature at which undesirablechanges in physical or chemical properties of the web take place. Thissurface temperature will, of course, be a function of both oventemperature and line speed where, for example, line speeds of 45feet/min. could be used for a paper web.

3,503,778 Patented Mar. 31, 1970 "ice The web then moves from thepreheat oven into a coating chamber where the coating chamber contains asaturated cloud of plastic particles which are to be de posited wherethe cloud is held under quasi-equilibrium conditions. That is, thefallout or coating rate of the power will be balanced by theintroduction of new powder. Coating thickness will be governed by linespeed and the rate at which powder is introduced into the chamber.

The surface temperature of the substrate will then soften some of thethermoplastic particles that fall upon the substrate to provide aninitial bond counteracting the effect of air currents generated by themoving substrate. If desired, this chamber can be longitudinallycompartmentalized to permit coating in diverse lengthwise patterns byshutting off various longitudinal compartments.

The dust cloud is then introduced through various feed ports in theforward wall of the chamber where these ports can be used in an desiredcombination to produce a proper coating distribution.

The web with the powder deposited thereon is then moved into a fusingoven which is located directly behind the coating chamber and containssuitable heat sources such as two or more fused quartz 4320 wattheaters, each governed by respective temperature controllers. Thetemperature of the fusing oven will then cause fusing of the depositeddust coating with the lowest possible increase in substrate temperature.The oven is preferably pressurized to prevent entry of loose dustparticles. It should be noted that the coating chamber will also operateunder a slightly positive pressure, again to prevent entry therein ofloose dust particles.

The final and essential component of the main system is the dust cloudgenerating device. The novel dust cloud generating device of theinvention is so constructed that the plastic powder loaded therein willbe agitated and suspended in space by means of a high volume, lowpressure flow of air. Escaping dust is then channeled through suitableconduits or hoses to the above noted settling or coating chamber.

Dust cloud density volume may be controlled by partially blocking theair intake of the blower supplying air to the interior of the dust cloudgenerator.

The dust cloud generator, in accordance with the invention, consists oftwo concentric wall sections which communicate with one another at thebottom of the chamber. The central chamber is then loaded with thepowder which is to be deposited, and two air sources are connected tothe unit; the first to the annular concentric chamber surrounding themain chamber, and the second to the interior of the main or centralchamber.

Air flow from the concentric chamber which surrounds the main chamberthen passes up through the bottom of the main chamber and through thebody of the powder contained therein. This operates in conjunction withair introduced into the interior of the chamber to generate a dust cloudwhich can then be taken out through suitable conduits into a settlingchamber.

Accordingly, a primary object of this invention is to provide a novelmethod and apparatus for the dry coating of plastic particles on asubstrate.

Another object of this invention is to provide a novel dust cloudgenerator which can create an evenly balanced dust cloud of plasticparticles of diverse densities and sizes.

Still another object of this invention is to provide a novel dustingprocess for dusting micro powders on a substrate wherein the processprovides a highly controlled feed and dispersion level of plasticpowders.

These and other objects of this invention will become apparent from thefollowing description when taken in connection with the drawings, inwhich:

FIGURE 1 schematically illustrates a particle dusting line constructedin accordance with the present invention.

FIGURE 2 is a cross-sectional diagram of the dust cloud generatorconstructed in accordance with the invention.

FIGURE 3 is a top view of the dust cloud generator of FIGURE 2.

FIGURE 4 is an exploded perspective view of the settling chamber used inFIGURE 1.

Referring first to FIGURE 1, there is illustrated therein a schematicdiagram showing the operation of a dusting line incorporating thepresent invention wherein a supply reel which could, for example, be aroll of paper which is to be coated, is stationarily mounted on arotating pivotal support 11 in the standard manner.

It is to be noted that while the invention is described herein withreference to the coating of paper, the invention has diverseapplications and could be applied, for example, to the coating ofstationary objects, or the coating of plastic webs, or the like.

The web 12 taken from reel 10 is first passed into a preheat oven stage13 which includes a suitable heating means (not shown) and a conveyorsystem comprised of conveyor belt 14 which circulates in the directionshown to carry the web 12 through the preheat oven 13 from left toright. Suitable doors or gates are provided at either end of the preheatoven to permit entry and exit of web 12.

The preheat oven 13 will cause an initial heating of the substrate ofweb 12 to prepare it for the settling of dust powders from the settlingor coating chamber 20. The settling chamber 20, which will be describedin more detail in FIGURE 4, is comprised of a substantially enclosedchamber having a removable top 21 which forms a dust-proof connection tothe top of chamber and has two openings therein 22 and 23 providingaccess for both web 12 and for a conveyor belt 24 which carries the webthrough the settling chamber.

A compressor 25 is connected to the top of chamber 20 to permit theapplication of low velocity air to the interior of the chamber to causea positive pressure therein, thereby preventing the entrance of freepowders into openings 22 and 23. Note that the right-hand end of chamber20 is provided with a baffle consisting of slidable plates 26, 27 and 28which permits pressure relief for air flow out of chamber 20 and throughexit opening 23 via a tortuous path. A vacuum chamber 30 may then beconnected immediately adjacent outlet opening 23 which will pick upexcessively loose powders which are deposited on web 12.

As will be described more fully hereinafter, three output conduits 31,32 and 33 from a dust cloud generator 34 are connected to the left-handend of settling chamber 20. After dust has precipitated on web 12 withinthe settling chamber 20, the web continues into a fusing oven 40 whichhas its separate conveyor belt 41 where the temperature within fusingoven 40 is sufficiently high to cause fusing of the powders depositedupon the web. Thereafter, the web is moved to a suitable windup stage 42where the web may be wound, a sufficient time being permitted forcooling of the plastic layer deposited atop web 12. Note that a suitablepair of nip rolls could be connected in front of windup stage 42 tocompact the fused layer of plastic on the top of web 12.

The dust cloud generator 34, described in FIGURE 1, is shown in moredetail in FIGURES 2 and 3. Referring now to FIGURES 2 and 3, it will beseen that the dust cloud generator is formed of a first outer steelcylinder 50 having a base 51 welded thereto. An outer annular chamber 52is then for-med by means of an interior cylinder 53 which is welded toupper disk 54 which is also welded to the outer cylinder 50. A metallicflow director 55 is then suitably fastened to base 51 which directs airflow from annular chamber 5211p into the interior of cylinder 53 whichis spaced from the top surface of base 51.

A head member 56 is then bolted to disk 54 as by suitable bolts 57 and58 where the head member 56 carries an input air conduit 59 and threeoutlet fittings 60, 61 and 62, which are connectable to hoses 31, 32 and33, respectively, of FIGURE 1. The top of annular chamber 52 is thenfitted with suitable conduits 63 and 64. Conduits 59 and 63 areconnected to the same compressor 65. Conduit 64 is then fitted with asuitable bleeding valve 66 to permit the bleeding of air pressure fromannular chamber 52.

In operation, the head member 56 is removed from disk 54 and theinterior cylinder 53, which may be approximately 25 inches high, isloaded with a suitable plastic powder to about /3 to /2 of its height. Asuitable plastic powder is polyethylene powder known by the trademarkMicrothene, which is a trademark of the National Distillers and ChemicalCorporation.

The head member 56 is then bolted in place with suitable gasketing means(not shown) forming an air-tight connection to the disk 54, andcompressor 65 is turned on to supply an air flow to conduit 63 andannular chamber 52 of approximately cubic feet/min. The air flowconnected to conduit 59 will be approximately 50 cubic feet/min; wherethe length of conduit 59 extending into cylinder 53 is approximately 10inches and falls short of the height of the plastic powder charge incylinder 53.

The pressures and air turbulence created in the interior of cylinder 53are then such as to cause a dust cloud having a slight over-pressure(with respect to the pressure of settling chamber 20), which dust cloudis conducted through conduits 60, 61 and 62 into their respective hosesconnected thereto and to the settling chamber 20 of FIG- URE 1.

The settling chamber 20 is further illustrated in FIG- URE 4 wherein thehoses 31, 32 and 33 are shown as connected to the left-hand end of thesettling chamber toward the top thereof.

As pointed out above, it has been found that, by arranging the dustcloud generator and settling chamber in the manner shown in FIGURES 2, 3and 4, dust of diverse particle sizes and densities will be suspendedwithin settling chamber 20 with a quasi-equilibrium wherein the amountof dust coming into the chamber is balanced by the amount settling onthe web carried through the chamber by conveyor 24. The amount of powderbeing brought out of the dust cloud generator can be controlled bysuitable control of the bleeding valve 66 of FIGURE 2 conduit 64 whichcontrols the pressure conditions within the dust cloud generator.

Although this invention has been described with respect to its preferredembodiments, it should be understood that many variations andmodifications will now be obvious to those skilled in the art, and it ispreferred, therefore, that the scope of the invention be limited not bythe specific disclosure herein.

What is claimed is:

1. A method of coating a substrate which comprises;

(a) generating a dust cloud of finely divided plastic particles bypassing a first flow of gas upward through a volume of plastic particles2 to 100 microns in size which are contained in a closed chamber to aheight less than the height of said chamber, and passing a second flowof gas into said chamber above the normal level of said volume ofparticles, (b) conducting said dust cloud to a settling chambermaintained at a pressure below the pressure in said first chamber, r

(c) preheating the substrate to a temperature abov the softening pointof the plastic particles,

(d) introducing said substrate into said settling chamber for a periodof time suflicient to permit a layer of said plastic particles to bedeposited on said substrate,

(e) maintaining the rate of introduction of the plastic particles intothe settling chamber in balance with the rate at which the materialsettles on the substrate, and

(f) heating the coated substrate to a temperature sufficient to causefusing of the plastic particles on said substrate.

2. The process of claim 1 wherein the plastic material is polyethylene.

3. The method of claim 1 wherein said plastic particles have a densitywithin the range of .910 to .965.

4. The process of claim 1 wherein said substrate is subjected topressure after heating.

References Cited UNITED STATES PATENTS Tinsley 11721 X Ballentine et a1.117-21 X Yarrison l1721 X Strobel 117-21 X Brooks 117-21 Bader et al117-21 X Brooks 11721 X Holt et al 11721 X Deyle et al. 11721 X US. Cl.X.R.

